U.S. Pat. No. 7,650,519 B1 describes a system and methods for connecting a graphic user interface to a powered network. The network-powered graphic user interface system converts encoded computer user interface signals transmitted over a powered network cable to multiple signal sets, each set associated with a peripheral device interface. Methods for managing the admission of the peripheral devices are also described. Connection criteria include the power budget for the connection, device characteristics, device power requirements and the characteristics of other devices sharing the powered network connection.
A commercially implemented system for providing power from a power providing device to multiple power receiving devices is the so-called “Power over Ethernet” (PoE), where the power providing device is called “Power Sourcing Equipment” (PSE) and the power receiving device is called “Powered Device” (PD).
For a PoE standard currently under consideration (IEEE 802.3bt) a scheme called “Autoclass” is discussed, being a classification mechanism that allows a PD to communicate its effective maximum power consumption to the PSE in such a way that the PSE will be able to set a power budget to the effective maximum PD power including the effective channel losses. An aim of this is a more efficient use of the available power as only the effectively used power is budgeted.
A possible process for this may have the steps of an controlled inrush (after a connection is provided by inserting a cable or the like), where the allocated power budget corresponds to the initially maximum possible power, of a maximal power consumption (after the PD started up) of the PD, with the PSE measuring the (maximum) power consumption, and finally of a reallocation of the power budget by the PSE for the PD based on the measure maximum power consumption (e.g. calculated by adding a margin accommodating for fluctuations of power requirements and measurement variations or errors).
Such autoclass approach allows, in comparison to the conventional power classes provided by PoE, for a finer granularity in the allocation of power and therefore for an improved power management.
However, still a problem exists with a number of PoE applications in which the PD power requirement is not stable over the lifetime but may vary. When the maximal power of the PD is growing over time, overload detection will trigger the PSE to switch off power provision to the PD.
Typical examples for PDs where this can happen are robotic systems where, for example, wear in the gear or aging grease increases moving resistance and subsequently the required power for the electrical drive. In lighting applications, a drop in LED efficiency and reduced optical quality of the luminaire may lead to increase input power need.
According to the method currently contained in the draft standard IEEE 802.3bt (in correspondence with earlier standards) a PD which needs more power than classed during its classification cycle will get switched off whenever its power drawn is above the overpower threshold the PSE has memorized. In a retry cycle the PSE will reclass the PD before it gets powered on again. For lamps in lighting applications this would mean that they would be turned off at a certain moment in time. As long as there is sufficient power budget reserve available the lamp can be restarted but an unpleasant flicker will irritate users of the illuminated space.
A straightforward possibility for addressing such increase in the power needs over time, so to avoid the switching off and on, may be to increase the margin appropriately such that even the increased power need still falls into the allocated power budget. Such approach, however, would offset the improved power management intended by the drafted standard IEEE 802.3bt.